1. Field of the Invention
The present invention relates to magnetically levitated (maglev) apparatus and more specifically to those magnetically levitating an impeller to deliver liquid such as blood.
2. Description of the Background Art
FIG. 7 is a vertical cross section of a maglev liquid pump apparatus as one example of a conventional maglev apparatus and a block diagram of a controller thereof. In FIG. 7 a magnetically levitated liquid pump apparatus 100 is configured with an electromagnet unit 120, a pump unit 130 and a motor unit 140 housed in a cylindrical housing 101. Electromagnet unit 120 has an electromagnet 121 and a magnetic bearing sensor 122 incorporated therein. Housing 101 has on one side a side wall having a center provided with an inlet 102 introducing a liquid. At least three electromagnets 121 and at least three magnetic bearing sensors 122 surround inlet 102. Electromagnets 121 and magnetic bearing sensors 122 are attached to a partition 103 separating electromagnet unit 120 and pump unit 130 from each other.
In pump unit 130 an impeller 131 is rotatably housed and it has a portion closer to electromagnet unit 120, or closer to one side, that is supported by electromagnet 121 contactless through partition 103, and magnetic bearing sensor 122 senses the distance as measured from one side of impeller 131. Impeller 131 has the other side with a permanent magnet 132 buried therein. Motor unit 140 houses a motor 141 and a rotor 142. Rotor 142 has a surface facing pump unit 130 and having a permanent magnet 143 buried therein, opposite to permanent magnet 132 buried in impeller 131, with partition 104 disposed therebetween.
In the liquid pump apparatus thus configured, magnetic bearing sensor 122 provides an output which is in turn input to a sensor circuit 201 included in a controller 200 and sensor circuit 201 detects the distance between one side of impeller 131 and magnetic bearing sensor 122. Sensor circuit 201 provides an output which is in turn input to a PID compensator 202 to provide PID compensation and PID compensator 202 provides an output which is in turn amplified by a power amplifier 203 and thus applied to electromagnet 121 to control attractive force provided toward the opposite side of impeller 131.
Furthermore impeller 131 has a portion closer to motor unit 140 that is affected by the attractive force introduced by permanent magnets 132 and 143 and impeller 131 is magnetically levitated by a non-controlled bearing provided by permanent magnets 132 and 143 and a controlled bearing provided by electromagnet 121. A motor control circuit 205 provides a control signal which is in turn applied to a power amplifier 204. Power amplifier 204 drives motor 141 and the motor""s driving force rotates impeller 131 and blood or any other similar liquid introduced through inlet 102 is output through an outlet (not shown) formed at pump unit 130.
The FIG. 7 magnetic bearing sensor 122 is a reluctance sensor using a carrier wave. This reluctance sensor is provided opposite to impeller 131 with the FIG. 7 partition 103 disposed therebetween. Note that partition 103 is formed of conductive material, particularly titanium for blood pumps owing to its compatibility with blood. The reluctance sensor generates a magnetic field, which introduces an eddy current in the conductive titanium and would thus impair the sensor""s sensitivity.
In order to avoid this the carrier wave is adapted to have a low frequency range. This, however, may significantly affect controlling the magnetic bearing. More specifically, a reluctance sensor using a carrier wave provides a detection with a phase delay for down to a frequency approximately two decades lower than that of the carrier wave, e.g., 100 Hz for a carrier wave frequency of 10 kHz. To compensate for this to reliably control the magnetic bearing, PID compensator 202 needs to be constructed to lead a phase to a high frequency range. Consequently PID compensator 202 has a gain increased and a component of the carrier frequency contained in the sensor output causes voltage saturation in a circuit portion internal to PID compensator 202 and thus prevents reliable control.
Therefore the present invention mainly contemplates a magnetic bearing apparatus capable of removing a carrier wave frequency component used in a magnetic bearing sensor, to provide reliably control.
Generally the present invention provides a magnetically levitated apparatus including: a drive unit driving and thus levitating a body to be levitated; a magnetic position detection circuit using a carrier wave signal to detect a position of the body as the body levitates; a controlled magnetic bearing unit operative in response to an output of the magnetic position detection circuit to support the body without contacting the body; a control circuit operative in response to a signal output from the magnetic position detection circuit to control the controlled magnetic bearing unit, wherein between the magnetic position detection circuit and the body there exists a partition formed of a conductive material; and a filter connected between the magnetic position detection circuit and the control circuit to remove a carrier wave signal output from the magnetic position detection circuit.
Thus in the present invention a filter can remove a carrier wave frequency component from a sensor output before amplification. Thus voltage saturation in the control circuit can be prevented to provide reliable control.
More preferably the magnetic position detection circuit includes: a reluctance sensor provided adjacent to the body and having an inductance varying as the distance between the reluctance sensor and the body varies; and a sensor circuit operative in response to an output of the reluctance sensor to output a signal varying as the inductance varies.
Furthermore the present apparatus further includes a carrier wave generation circuit feeding the magnetic position detection circuit with a carrier wave signal, wherein: the sensor circuit outputs the carrier wave signal with the amplitude varying as the spacing between the magnetic position detection circuit and the body varies; and the filter removes a center frequency of the carrier wave signal.
Furthermore the filter is a band eliminating filter arranged immediately subsequent to the sensor circuit.
Furthermore, the drive unit includes a non-controlled magnetic bearing unit magnetically coupled with the body at one side and a drive unit operative to rotate the body via the magnetic bearing unit, and the controlled magnetic bearing unit is magnetically coupled with the body at the other side.
Furthermore the body is an impeller rotated to output a liquid and the magnetically levitated apparatus configures a magnetically levitated pump.
The magnetically levitated apparatus further includes a drive unit rotatably driving the impeller through magnetic-coupling.
Furthermore the impeller is rotated to output blood and the magnetically levitated apparatus configures a blood pump apparatus.
Furthermore the impeller is rotated to output blood and the magnetically levitated apparatus configures a blood pump apparatus.
More preferably the body is rotated to rotate a vane and the magnetically levitated apparatus configures a turbo molecular pump.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.